An optical recording medium allows recording various signalized information to optically reproduce. There are various kinds of recoding type such as: read-only type optical discs in which embossed pits corresponding to data are preformed on a disc substrate, such as compact discs and laser discs; magneto optical discs on/from which data is recorded and reproduced utilizing a magnetooptical effect, such as Mini Discs (MD); and phase-change optical discs on/from which information (data) is recorded and reproduced utilizing phase change of a recording layer, such as Digital Versatile Discs (DVD).
In the optical recording medium capable of rewriting information, such as magneto optical discs and phase-change optical discs, contiguous grooves instead of discrete pits are formed along a recording track. The grooves are provided for mainly controlling tracking servo, so-called guide grooves. The interspaces between the grooves are called lands because they protrude in the position close to the surface of the grooves than the bottom thereof.
The optical recording medium formed with the grooves generally performs a tracking servo control by using a push-pull signal. In order to obtain the push-pull signal, a light beam is irradiated toward the optical recording medium and the light reflected by the optical recording medium is detected with two photodetectors placed symmetrical to the center of the track, thereby the push-pull signal can be obtained based on a difference in the outputs from two photodetectors.
The applicant has proposed a method of forming wobbling wide grooves, which is a data recording area of MD, by superimposing the signals of 22.05 kHz and 5 MHz in Japanese Patent No. 2960018. In this method, FM modulation signal of 22.05 kHz is for recording wobble information of address, whereas the signal of 5 MHz is for widening the groove width in accordance with the amplitude. With this method, the wobbling wide grooves are formed to wobble both sides of the grooves. The data recording area becomes wide grooves by forming the wobbling wide grooves in the optical recording medium. This achieves the stable reproduction of wobble signal of ADIP and the stable recording/reproducing of MO signal.
Japanese Patent No. 2854187 proposes the technique that one side of the grooves is wobbled and the other side is not wobbled but in straight (circular arc). According to the technique, address information can be stored in the wobbles of the grooves.
A high recording density and the stable reproduction of the wobble signal are required in the optical recording medium formed with the wobbling grooves.
However, in the optical recording medium in which one side of the grooves are wobbled as disclosed in Japanese Patent No. 2854187, the other side of the grooves which is not wobbled is not used for storing the address information. As a result, the wobble signal amount is about half of the optical recording medium in which both sides of the grooves are wobbled, thereby resulting in a problem of the difficulty of the stable reproduction of the wobble signal.
In addition, the stable reproduction of the wobble signal is desired by increasing the wobble signal amount. However, in order to form the grooves in which both sides thereof are wobbled and to improve the recording density, it is necessary to narrow a track pitch. The narrow track pitch generates beats in the wobble signal between the neighboring wobbles specifically in case of an out-of-phase wobble. This results in the problem of the difficulty of the stable reproduction of the wobble signal.
The present invention has been achieved in view of the above problems. It is an object of the invention to provide an optical recording medium capable of stably reproducing the wobble signal without generating beats even if the track pitch is narrowed to improve the recording density. Further, the present invention provides an optical recording/reproducing apparatus used for recording/reproducing on/from the optical recording medium, an optical recording medium master used for replicating the optical recording medium and an apparatus for manufacturing optical recording medium master.